1. Field of the Disclosure
The present disclosure generally relates to seismic prospecting and in particular to methods and apparatus for conducting seismic surveys.
2. Description of the Related Art
In the oil and gas exploration industry, geophysical tools and techniques are commonly employed in order to identify a subterranean structure having potential hydrocarbon deposits. Many different techniques are used to generate a seismic signal.
Seismic vibratory energy sources have been used in the field many years. A seismic vibrator in its simplest form is merely a heavy vehicle that has the ability to shake the ground at a predetermined range of frequencies of about 2 to 300 Hz. The vibrator imparts a signal into the subsurface of the earth over a relatively long period of time, which allows for an energy level less than an impulse generator such as dynamite. In some applications, a seismic vibrator may also be used as a surface impulse source.
The imparted energy, known as the seismic source signal or “pilot” signal, travels through the subsurface and reflects some of the energy from certain subsurface geological boundaries or layers. The reflected energy is then transmitted back to the earth's surface where it is recorded using an earth motion detector. The recorded data is processed to yield information about a location and physical properties of layers making up the subsurface. The seismic vibrator source signal is typically a sweep signal, or simply sweep.
Conventionally, the vehicle weight provides an assumed static force load that maintains continuous contact between the base plate and the underlying earth. If the static force, or “hold-down” force, is insufficient, then the base plate may decouple from the earth, which may lead to signal to noise level degradation. If the static force exceeds the effective vehicle weight, then the vehicle may become unstable.
The present disclosure provides methods and devices for improving seismic sweeps by compensating for factors affecting the magnitude of the hold-down pressure applied to the base plate.